java - Doubly Linked List Null Pointer Exception -

i'm trying work on remove function doubly linked list, keep getting null pointer exception on current.prev.next = current.next; part. don't think understand null pointer exception is, because have no idea fix this. log function 1 wrote write output file, , retval[1] element i'm searching delete.

node current = head;      while(current != null)     {             if((current.data).compareto(retval[1]) == 0)             {                     if(current.prev == null)                         head = current.next;                      if(current.next == null)                         tail = current.prev;                      current.prev.next = current.next;                     current.next.prev = current.prev;                      current = null;                      valid++;                     log(line + "\n" + "sucsessfully removed \n");              }             else             {                 log(line + "\n" + invalidtransaction + " - element not exist \n");                  }              current = current.next;         } 

i'm sure it's stupid, don't know is. appreciated.

just replace

current.prev.next = current.next; current.next.prev = current.prev; 

with

if(null != current.prev) current.prev.next = current.next; if(null != current.next) current.next.prev = current.prev; 

and need break loop once element found.